Titanium-base alloys

ABSTRACT

ALLOYS OF THE TITANIUM PLUS 1.5-3.5% COPPER TYPE, SUITABLE FOR STRIP AND SHEET MANUFACTURE, ARE GIVEN INCREASED STRENGTH, WITHOUT DETRIMENT TO THEIR OTHER PROERTIES, BY THE ADDITION OF UP TO 5% IN TOTAL FROM THE GROUP OF 0.25-5% OF ALUMINIUM, ZIRCONIUM AND TIN AND 0.1-1 SILICON. THE ALLOYS ARE AGE-HARDENABLE.

United States Patent US. Cl. 148-325 4 Claims ABSTRACT OF THE DISCLOSURE Alloys of the titanium plus 1.5-3.5% copper type, suitable for strip and sheet manufacture, are given increased strength, without detriment to their other properties, by the addition of up to 5% in total from the group of 0.25-5% of aluminium, zirconium and tin and 0.1-1 silicon. The alloys are age-hardenable.

This is a continuation of application Ser. No. 836,625, filed June 25, 1969, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to titanium-base alloys and in particular to alloys suitable for the manufacture of sheet and strip.

A titanium alloy suitable for sheet having moderate strength has been known for some years, and this alloy is a binary alloy containing nominally 2.5% copper. The ductility of the alloy is satisfactory for forming operations and welding can be carried out without adversely affecting ductility. The alloy is age hardenable to an ultimate tensile strength of about 50 tonf./sq. in. under certain conditions but such a level of strength is not adequate for certain applications and no alternative sheet alloy with a suitable combination of properties exists.

We have found that the composition of the abovementioned alloy can be so modified that a higher strength can be obtained without detriment to other properties, in particular, formability.

SUMMARY OF THE INVENTION DESCRIPTION OF THE PREFERRED EMBODIMENT Ternary alloys within the above ranges have been pre-. pared containing elements in the following amounts:

Titanium-2.5% coppen+0.5, 1.0, 1.5, 2.0 and 3.0%

aluminium Titanium-2.5% copper+lJ0, 3.0 and 5.0% zirconium Titanium-2.5% coppen+1.0, 3.0 and 5.0% tin Titanium-2.5% copper-i025 and 0.5% silicon Quaternary alloys containing the following have been prepared:

Titanium-2.5% copper+0.5, 1.0 and 1.5% aluminium zirconium Titanium-2.5% copper+0.5, 1.0 and 1.5% aluminium !+0.25% silicon Other alloys prepared include:

Titanium-2.5% copper-1.0% zirconium-0.25%

+0.5, 1.0 and 1.5% aluminium.

silicon 3,746,585 Patented July 17, 1973 ice Percent Aluminium 1.53.0 Zirconium 1.03.0 Silicon 0.25-0.5

and these are the preferred ranges.

The addition of the elements mentioned herein to the basic titanium-2.5% copper alloy has been found to suppress the increase in hardness during aging if the amounts specified are exceeded. The addition of up to 5% tin completely suppresses age hardening in titanium- 2.5% copper. Within the limits specified, improvement in tensile properties can be obtained and in the preferred compositions, the maximum increase is obtained.

Titanium alloys normally contain carbon, oxygen and nitrogen as impurities and in the alloys in accordance with the invention, carbon and nitrogen are maintained at normal impurity levels but oxygen may be present up to 0.25% with advantage, since the tensile strength is thereby increased by 3 to 4 tonf./in. without significantly affecting ductility. Oxygen is normally present in the range 0.130.l8%.

The preferred alloys having a good combination of properties are those having the following compositions:

Titanium-2.5% copper-1.5% aluminium Titanium-2.5% copper-2.0% aluminium Titanium-2.5% copper-1.0% aluminium-1.0% zirconium- 0.25 silicon.

, Alloys in accordance with the invention are age hardenable after solution treatment at a temperature of 775 C. or more depending upon the composition. The preferred alloys are solution treated at 8l0820 C. and the aging temperature is in the range 425-450 C.

In heat-treatment tests on the preferred alloys, maximum hardening was obtained by aging at 425 C. The highest aging response was observed on titanium-2.5% copper-1.5 aluminium, which increased in strength from 44.5 tonf./in. to about 57 tonf./in. an increase of 12.5 tonf./in. On the other hand, the titanium-2.5% copper- 2.0% aluminium alloy, which had a solution treated strength 4.5 tonf./in. higher than the 1.5% aluminium alloy, only increased in strength by 8.5 tonf./in. from 49.1 tonf./in. to 57.6 tonf./in. The quinternary alloy had a solution treated strength of 47.1 tonfJin. and exhibited an aging response of some 11 tonf./in. Although a fall in reduction of area values was evident after aging, all three alloys possessed high ductility at the maximum strength level.

Age-hardening characteristics of the three alloys at 425C. were quite different. Tensile strength of the titanium-2.5% copper'l.5% aluminium alloy tended to increase progressively with aging time and was accompanied by the steady growth of a coherent precipitate zv2hsicghcwas about 600 A. in length after 192 hours at The titanium-2.5% copper-2.0% aluminium alloy did not increase in strength to any extent during the first 72 hours at 425C. and then appeared to increase quite significantly in the next 48 hours. The number of nuclei formed in this alloy appeared to be smaller than on titanium-2.5% copper-1.5% aluminium, but their rate of growth seemed to be more rapid, precipitates being around 800 A. in length after 192 hours at 425 C.

In contrast to the ternary titanium-copper-aluminium alloys, titanium-2.5% copper-1.0% aluminium-1.0% zirresponse. Non-coherent overaged precipitates of 1500 A.

and 2500 A. length were noted in the 1.5% and 2.0% aluminium alloys after 96 hours at this temperature. On the other hand precipitates in the zirconium-silicon bearing alloys were coherent and 650 A. in size.

After 96 hours at 450 C., precipitates in all three alloys were non-coherent and larger than those formed after a similar time at 435 C.

The intended use of alloys in accordance with the invention is as sheet, and it is desirable that sheet should have adequate bending properties and good weldability in addition to good tensile strength. The preferred alloys possess such as combination of properties.

A summary of properties after solution treating at 820 of the preferred alloys are consistent with this value having regard to their higher tensile strength.

The properties of solution treated and welded, and of welded and aged sheet, tested with the weld transverse to the test piece axis were quite satisfactory, and revealed no evidence of embrittlement in the weld area.

The preferred alloys have considerably greater tensile strength than the titanium-2.5% copper alloy and increases in strength of up to 10 tonf./in. have been observed. With oxygen contents of up to 0.25%, sheet alloys having a tensile strength of 60 tonf./in. and over are obtainable.

Adequate ductility is maintained'in these alloys and with the highest tensile strengths elongation values of about 17-18% can be expected. The alloys are cold formable.

When heat-treated, alloys according to the invention exceed 55 tonf./in. which is 10% greater than the nominal 50 tonf./in. of the binary alloy and dependent upon composition, may reach 20% greater tensile strength.

Elevated temperature tensile tests show that the alloys of the invention have appreciably higher strength at 300 C. and 400 C. after heat-treatment compared with the binary alloy.

TABLE I Solution treated properties Properties after aging at 425 0.

Percent Percent Agm 0.1% 19s, '1 42 RA, 0.1% PS, 'r 8 RA, perio Alloy tout/1n." tent/m I 4 #80 percent tout/in. tent/in. 4 {5 6 percent (hrs.) Test piece Tl-2.5 (Eu-1.5, Al 32. 7 44. 5 26 31 46. 9 57. 6 20 27 192 R 11 d a r-2.51 (Eu-2.0, Al s5. 7 49.1 21 34 41. 4 57. o 20 32 144 0 1 30, Ti-2.5, Cu-1.0, Al-LO, Zr-0.25, Si. 35.3 47. l 19 44.3 58.3 23 31 192 Do. Ti-2.5, ou 31. 2 42. a 20 47 40. 0 51. 5 24 40 24 hrs. at 400 0. and

8 hrs. at 475 0.

TABLE II Percent Limiting 0.1% PS, 0.2% PS, TS, elong. bend Nominal composition, weight percent Heat-treatment procedure Test material tonL/in. tent/in. tent/in. on 15 in. radius t Ti-2.5, Cu-1.5, Al Soggi og tr a ted hr. at Parent sheet 29.3 31. 4 39. 6 20 3.0

Solution treated and aged --d0 52.7

168 hrs. at 425 0. Solution treated and Weld transverse to 34. 8 35. 9 41. 4

welded. test piece axis. do Weld parallel to test 42. 5

piece axis. Solution treated, welded, Weld transverse to 50. 9

aged 168 hrs. at 425 0. test piece axis.

Ti2,5, 011-2, Al Solution treated hr. at Parent sheet 37.1 37. 2 44.0

820 0. AC. Solution tseated and Weld transverse to 36.0 36. 8 42. 9

welded. test piece axis. do Weld parallel to test 45. 2

piece axrs. Solution treated, welded Weld transverse to 52. 1

and aged 168 hrs. at test piece axis. 425 C.

Tl-2.5, Cu-l, Al-l, Zr0.25,Sl sobiztiorci tristed 56 hr. at Parent sheet 37. 1 37.4 44. 4 26 2. 5

Solution treated and aged do 55. 1 18 168 hrs, at 425 0. Solution treated and Weld transverse to 35. 3 26. 7 44. 4 e 10 3. 2

welded. test piece axis. do Weld parallel to test 46. 7 26 piece axis. Solution treated, welded Weld transverse to 55. 8 14 test piece axis.

and aged 168 hrs. at 425 C.

' Parent sheet failure at end of gauge length.

b Fractured outslde gauge length.

Norm-All tests transverse to final sheet rolling direction except those with weld parallel to gauge length.

C. in the case of ternary alloys or 810 C. in other cases and after age hardening is given in Table I. Tests were made on rolled rod to facilitate test piece manufacture. Tests made on sheet, including welded sheet, are shown in Table H. The limiting bend test indicates the minimum radius, expressed as a multiple of the thickness of the sheet, around which the test piece could be bent cold without cracking.

By way of comparison it should be mentioned that titanium-2.5% copper, when heat-treated to a tensile strength of about tonf./in. can be bent around a radius of 3 times its thickness. The bending properties 0.25% oxygen.

5 6 3. A titanium-base alloy as in claim 1 containing 771,952 4/1957 Great Britain 75-175.5 2.5% copper, 1.0% aluminum, 1.0% zirconium, 0.25% 1,108,039 3/1968 Great Britain 75--175.5 silicon, balance titanium apart from impurities. 594,813 3/1960 Canada 75-175.5

4. A titanium-base alloy as in claim 1 solution treated at 810820 C. and aged at 425-450 C. 5 OTHER REFERENCES R f en Cited WADC Technical Report 58-328, Development of UNITED STATES PATENTS liKSlZlilTliliCiZ??? Base Alloys, October 1958, pp. 1-7,

9 9 2,868,640 1/l959 Butler 75--175.5 2,867,534 l/ 1959 Jaffee et a1. 75-175.5 10 CHARLES LOVELL Primary Examiner 2,777,768 1/1957 Busch et al. 75---175.5

FOREIGN PATENTS 653,682 12/1962 Canada 7s 175.s 75"175'5;148 133 1,057,578 2/1967 Great Britain 7s 175.s 15

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,74 ,535 Dated Julv 17. 1973 Inventor(s) RICHARD ERNEST GOOSEY It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading, after "This application Dec. 7, 1971,

Ser. No. 205,728" insert --Claims priority, Application Great Britain, July 1, 1968, 3l369/68--.

Signed and sealed this ll th day of May 197b,.

(SEAL) Attest:

EDWARD M.FLETGHER,JR. I C. MARSHALL DANN Attesting Officer Commissioner of Patents foam 9. uscoMM-oc wan-ps9 

